Control for self-advancing hydraulic roof supports for longwall faces in mines

ABSTRACT

An improvement in a traveling mine roof support wherein hydraulically at least two frames are moved forward in response to hydraulic pressure, said frames being connected to a piston maintained within a cylinder, said system including means for feeding fluid under pressure into the face side of cylinders holding the frames while one of the frames is maintained immobilized between a mine floor and a mine roof. The device provides means for advancing the frames, one after the other, while one of the frames is stationary. Check valves are provided to open the hydraulic lines. Valves are also provided in the event the pressure in the system exceeds predetermined values.

United States Patent 1 Grebe 3,724,329 Apr. 3, 1973 [54] CONTROL FOR SELF-ADVANCING HYDRAULIC ROOF SUPPORTS FOR LONGWALL FACES IN MINES Primary ExaminerPaul E. Maslousky AttorneyBurgess, Dinklage & Sprung [76] Inventor: Konrad Grebe, Kaiser-Wilhelm-Al- [57] ABSTRACT 1ee,wPPe1'talElbel'fe1d,Germany An improvement in a traveling mine roof support [22] Filed: Sept 2, 1970 wherein hydraulically at least two frames are moved forward in response to hydraulic pressure, said frames [21] Appl' 68,829 being connected to a piston maintained within a cylinder, said system including means for feeding fluid [52] 11.8. CI. ..9l/189, 91/217, 91/417 under pressure into the face side of cylinders holding [51] Int. Cl. ..F0ll 15/00, FOlb 15/02 the frames while one of the frames is maintained im- [58] Field of Search ..9l/17O MP, 189, 417 mobilized between a mine floor and a mine roof. The device provides means for advancing the frames, one References Clted after the other, while one of the frames is stationary. UNITED STATES PATENTS Check valves are provided to open the hydraulic line s. Valves are also provided in the event the pressure in 2,859,022 11/1958 Frye ..91/170 MP th tem ex eeds predetermined values. 3,272,084 9/1966 Bolton et al. ..9l/l70 MP 5 Claims, 6 Drawing Figures 22 4 22 g l I I 2; ZZI Z2; g; I\ l FiQ FE /05' 9 302' I 1 9 2) i L f i l 3 Out; i l l )l 1, 209 301 T I 24O/2Oat h v 2O/24Oa 4 5% I +-4- 235 235'4 741 I J 209 l "4- 1423 i 1 "N l2 1 r 231? 53 234 [17 l l I @91 1 i l 8 71 Z40/Out 2 1 l a 10 '5' l 1 240ut 1- 2401116 l s w l t t a s I t s s s g s s S k l 326 326 Q CONTROL FOR SELF-ADVANCING HYDRAULIC ROOF SUPPORTS FOR LONGWALL FACES IN MINES Improvement over the travelling mine roof support of U.S. application Ser. No. 719,334 filed Apr. 8, 1968, now US. Pat. No. 3,541,926, sufficient to speed the operation thereof by substantially continuously moving a conveying or winning means forward while maintaining positive roof support. The apparatus includes at least two frames A and B which alternately support the mine roof with each frame having a cylinder with a mine face side chamber and a back side chamber separated by a piston and piston rods associated with and connected to conveying or winning means associated with suitable hydraulic lines, valves, including step limiting assembly means adapted to equally reduce the feed to the back side chambers through appropriate lines, and pumping means sufficient to sequentially:

a. feed high pressure hydraulic fluid into the face side chamber of the cylinders of said frames A and into the back side chamber of the cylinders of said frames B while maintaining said frames B immobilized between a mine floor and a mine roof whereby releasing the roof supporting position of frames A, advancing said frames A to the conveying or winning means, and additionally advancing said conveying or winning means, frames A and the piston rods of both frames while maintaining said frames B stationary;

b. feed high pressure hydraulic fluid into the back side chamber of the cylinders of both of said frames A and frames B whereby to set frame A and to advance said conveying or winning means and said piston rods while maintaining all frames stationary;

c. feed high pressure hydraulic fluid into the back side chamber of the cylinders of said frames A and into the face chamber of the cylinders of frames B while maintaining said frames A immobilized between said mine floor and said mine roof whereby releasing the v roof supporting portion of and advancing said frames B to said conveying or winning means and additionally advancing said conveying or winning means, frames B and the piston rods of both frames while maintaining said frames A stationary;

d. feed high pressure hydraulic fluid into the back side chambers of the cylinders of both frames A and B whereby setting said frame B advancing said conveying or winning means and said piston rods while maintaining all of said frames stationary;

e. and repeating step (a).

This invention relates to a control system for self-advancing hydraulic roof supports for longwall faces in mines.

In prior Patent application Ser. No. 719,334 filed Apr. 8, 1968 there is disclosed a system for controlling, from a central control station containing means for generating hydraulic pressure, self-advancing hydraulic roof supports for longwall faces in mines. These roof supports comprise pairs of parallel multi-prop frames A and B, wherein the props of one frame of each pair are connected to a first hydraulic line and the props of the other frame of each pair are connected to a second hydraulic line. Each of said lines functions alternately as a pressure supply line and/or as a return line. The connecting pipes to said lines each contain a controllable check valve so arranged that the control piston of each check valve associated with one of the frames of each pair is controlled by the pressure existing in the line which serves the props of the other frames of each pair or by the pressure existing in another hydraulic line for operating ram cylinders which alternately advance the frames of each pair. The pressure in the first or second line, whichever functions as a return line, is kept at a selected holding level for elastically maintaining contact between the props and the roof during advance of the frames.

The present invention has the aim of further developing the control system proposed according to the above Patent application Ser. No. 719,334, and constitutes an improvement in or modification of the invention described and/or claimed in the said Application.

In order that it may be applicable to a self-advancing supporting structure of the latter-mentioned kind, this invention proceeds from an embodiment of this control system in which the frames A and B each overtake and progress past one another. In this embodiment of the apparatus represented in FIGS. 5 9 of the above referred to prior Application, the props of the frames A are caused to communicate, by way of controllable check valves, with a main hydraulic line 1 which alternately serves as hydraulic line and as a hydraulic return line in the consecutive cycles of the advancing motion of the supporting structure, while the props of frames B are caused to communicate in an analogous manner with a similar main hydraulic line 2. Thus, these hydraulic lines are utilized for setting the props and, when the check valves are in their opened condition, for relieving the props. In fact, a pressure of preselected magnitude is maintained in these hydraulic lines even while they are in their relieved condition, so that sensing contact of the roof-supporting caps or beams will continue to be established with the mine roof of the seam even while the frames are being advanced.

As soon as one relieved main hydraulic lines is subject to the full pressure of the hydraulic system, the other main hydraulic line may be relieved of pressure. The fact that one of these main hydraulic lines 1 or 2 is relieved of hydraulic pressure at the beginning of each advancing cycle causes, in accordance with the prior referred to Application, a hydraulic line, which controls the said check valves associated with the pressurerelieved main hydraulic line, to be acted on by the hydraulic system pressure and to open these check valves. It also causes the advancing cylinders which are associated with the particular pressure-relieved frame A or B and which hold or drive these frames to be advanced in the direction of the long-wall face. According to the prior referred to Application, the latter-mentioned control procedures are brought about by virtue of the fact that, following the action of relieving the main hydraulic line 1 or 2 (which pressure relief is intended to be carried out at a main control station), the main hydraulic lines 4 or 5, which act on the advancing cylinders of the frames A or B and which control the check valves in the main hydraulic lines 1 or 2, are themselves acted on by the hydraulic pressure medium in the main control station. It lies fully within the scope of the teaching of the prior referred to Application that the switching actions which follow the action of relieving the main hydraulic line 1 or 2 will also be initiated for example for the purpose of realizing a sequence control action by valves which are associated with the individual frames of the supporting structure.

The present invention is concerned with solving the problem of providing, by means of a control excercised in accordance with these principles, a continuous advancing motion of mining equipment and/or of a conveyor device along the long-wall face. This involves a consideration of various factors among which is that, if mining equipment or a conveyor device is rigidly connected to the frame A or to the frame B, then it will not be possible for each of frames A and B to overtake and pass one another, since the forward motion executed by the mining equipment or by the conveyor device through the advance of one frame, for example A, limits the possible degree of forward motion of the other frame, for example frames B. Thus, frames B can only be brought to that point or level already attained by frames A, and frames A have to be set or immobilized during the period during which frames B are catching up with frames A so that a break has to occur, during this period, in the advancing motion of the mining equipment or conveyor device connected rigidly to these frames A.

It has already been proposed, for the purpose of eliminating this break, to shiftably connect the mining equipment or the conveyor device to the frames A as well as to the frames B. The released frames B can thus be moved forward by the mining equipment or conveyor device, which themselves are advanced by the set or immobilized frames A, and during this time these released frames B can also be brought by their advancing cylinders into abutting contact with the mining equipment or conveyor device, which they had thrust away from themselves in the preceding working stage as a result of the outwards movement of their pistons from their associated advancing cylinders. Thus, at the end of each cycle of advancing motion, the released frames are once again brought into contact with the mining equipment or conveyor device as a result of their pistons being once again retracted into their respective cylinders, while the set or immobilized frames have thrust the mining equipment or conveyor device away from themselves as a result of the outward movement of their pistons in their associated advancing cylinders. When the hitherto released frames are set or immobilized and the hitherto immobilized frames are released, this sequence of events is repeated. In other words, the released frames are each advanced by two steps or paces, while the mining equipment or conveyor device is advanced by one step or pace by the immobilized frames, so that the released frames draw up into alignment with the reset frames during each cycle of advancing motion. If the released frames were located at the start of the advancing cycle one step to the rear of the set frames and, if they advance twice as fast as the mining equipment or conveying device, they will lie one step in front of the set frames at the end of each advancing cycle.

A modified control system which does not belong to the prior art and which is based on the general principles of the prior referred to application similarly entails a hiatus (although it is a much shorter one) in the advance of the mining equipment or of the conveyordevice because a certain time must elapse between each two successive advancing cycles before the hitherto released frames can be reset. Also, the hitherto set frames cannot be released before the hitherto released frames have been reliably reset, because otherwise the whole working face might well collapse. When carrying out procedures which enable particularly quick mining progress to be realized, such regularly-repeated, short breaks in operation can have a very obstructive effect because they prevent the continuous utilization of the conveying capacity which in any case is subject to very high loads, and because they also prevent a uniform utilization of the large quantities of air which are required for effecting a rapid advance motion.

In accordance with the basic principle of the control system proposed according to the present invention, this problem is solved by virtue of the fact that each advancing cycle in which the conveyor device or the guide of the mining equipment is uniformly advanced by the advancing cylinders associated with the immobilized or set frames B (A) is divided into two component phases. In the first of these phases, the frames A (B) are released and are brought up to the level of the conveyor device or to the level of the guide means of the mining equipment, and in the second of these phases the frames A (B) are being set or immobilized while, simultaneously, the advancing pistons rods of the cylinders associated with the frames A (B) which are to be immobilized (the pistons rods of all cylinders having a correspondingly greater length of working stroke) are so acted on by the hydraulic pressure medium that, under the effect of step limiting assemblies, they are moved outwardly of their associated cylinders at the same speed as the advancing pistons rods of the cylinders which are associated with the immobilized frames B (A).

When, at the end of the advancing cycle, the piston rod has moved to its full extent outwardly of its associated advancing cylinder (this advancing cylinder being itself associated with the frames B, the frames A will thus be subjected to the full pressure of the hydraulic system, and the next advancing cycle can immediately start by the frames B being released and caused to attain the level of forward motion already attained by frames A. The periods of time during which frames A are immobilized and during which frames B are immobilized (or vice versa) no longer follow one another in succession but overlap one another. Due to this overlap and due to the additional length of working stroke of the piston rod of the advancing cylinders this additional length of the piston rod working stroke being proportional to the said overlap time the advancing motion of the conveying or winning device can proceed without any breaks. If it is assumed that the step-limiting assemblies cause the mining equipment to be advanced by one millimeter per second and if it is also assumed that each advancing cycle lasts for 40 seconds, then the mining equipment will be advanced by 40 mm in each advancing cycle. When the system according to the prior referred to Application was employed, the pistons of the advancing cylinders had a working stroke of 40 mm. According to that system the advancing cylinders associated with the immobilized frames and securely connected thereto were exactly drawn up into contact with the guide means of the mining equipment at the start of the advancing cycle, so that their pistons were in their completely retracted position. At the beginning of the advancing cycle, the released frames lay 40 mm to the rear with the pistons of their advancing cylinders in their fully outwardly-extended positions. At the end of the advancing cycle, the pistons of the advancing cylinders associated with the immobilized frames were thus fully extended from these cylinders, the pistons of the advancing cylinders associated with the released frames were fully retracted into these cylinders, the mining equipment was advanced through a distance of 40 mm during the advancing cycle, and the originally released frames had moved forwards through a distance of 80 mm. A break in operation of, for example 20 seconds, was now necessary prior to the start of the next advancing cycle so as to ensure that, prior to releasing the hitherto set frames (that is the now rearwardly positioned frames), the hitherto released frames would be completely set. The exact length of this break in operation depended on the length of the longwall face and on the capacity of the pump which fed the main hydraulic lines 1 and 2. As an example, however, this break can restrict the advance of the mining equipment from a maximum of 3,600 mm per hour, at the above rate, to at most 2,400 mm per hour where the breaks are of 20 seconds duration and to about 2,600 mm per hour where the breaks are of seconds duration.

Without, however, altering the total duration of the advancing cycle (e.g. 40 seconds) or the speed of advancing motion (eg 1 mm per second), this invention makes possible 90 advancing cycles per hour instead of the 60-66 cycles it has hitherto been the practice to use. Therefore, a forward speed of 3,600 mm/hour becomes possible. In the case of the two selected reference examples given above, the overlap time during which both frames are set is and 15 seconds respectively, while the additional working stroke length of the pistons is accordingly 20 and 15 mm respectively; that is to say, each piston can new travel a distance of 60 or 55 mm respectively, instead of the 40 mm which was hitherto the case, out of its associated cylinder.

When a position is reached in which the pistons of frames A are fully extended from their cylinders, then the guide means of the mining equipment will lie a distance of 60 to 55 mm respectively in front of the advancing cylinders of frames A which are still in their set condition and, accordingly, 20 or 15 mm respectively in front of the advancing cylinders of the frames B which have already been set. As the pistons of the frames A have completed their outwardly directed working stroke, a new advancing cycle must now commence. Accordingly, the frames A are released and the frames B, which have already been set during the overlap time, immediately assume the function of causing the further advancing motion of the mining equipment. This new advancing cycle lasts 40 seconds. The last 20 or 15 seconds respectively of this advancing cycle represent the overlap period in which neither the frames A nor the frames B move. Prior to this overlap time there are thus 20 or seconds respectively available during the overlap period during which the frames A have to be released. However, during these 20 or 25 seconds the frames A are advanced by a total of 80 mm which is made up as follows:

1. 40 mm. This is the distance required to bring frames A into alignment with frames B;

2. 20 or 25 mm. This is the advancing motion which the mining equipment executes, in the meantime, relative to frames B;

3. 20 or 15 mm. This is the distance covered for eliminating the distance which was hitherto present between the frames A and the mining equipment, this distance covered being the result of the excess working stroke length of the pistons.

At the end of the 20 or 25 seconds, the mining equipment is 20 20 mm (or 25 +15 mm), that is to say, 40 mm in front of the advancing cylinders of the immobilized frames B, while the advancing cylinders of the released frames A now directly about the guide means of the mining equipment. They therefore no longer lie 40 mm to the rear of the advancing cylinders of the frames B but 40 mm in front of these advancing cylinders. 20 or 15 seconds respectively will elapse before the advancing cycle is ended, and the frames A will be reset during this time.

As the mining equipment is still being advanced by the frames B during this time, frames A are relieved of any stress which might have resulted from this advancing motion and still remain, at the commencement of the setting operation, at the point which they have atrained. This relief of stress is enhanced by virtue of the fact that the chamber of each advancing cylinder of frames A which is used for thrusting the pistons outwardly of their associated cylinders, is charged with hydraulic pressure medium at the same rate as the corresponding chamber in the advancing cylinders which are associated with the frames B and which are subjected to the full pressure of the hydraulic system.

Thus, at the end of the advancing cycle a position is reached in which the pistons of the advancing cylinders associated with the frames B are in their fully extended positions, while the guide means of the mining equipment lies 20 or 15 mm in front of the advancing cylinders of the frames A which have already been set. The same sequence of events can be continuously repeated and it is clearly possible to divide each advancing cycle into two component phases of any length, subject to the condition that the length of the first of these phases suffices to release frames A or B and to advance them a distance which corresponds to twice the distance of the forward motion of the mining equipment during an advancing cycle, and subject to the further condition that the additional working stroke length of the piston of the advancing cylinders permits the length of the second phase of the advancing cycle to be equal to the length of time required for reliably setting the props of all the released frames A or B to which there is now applied the maximum hydraulic pressure which the system can generate.

An example of a control system in accordance with the invention isshown in the accompanying drawings, in which:

FIG. 1 is a schematic view of the operating principles of this invention.

FIGS. la, 2, 3 and 4 show pairs of frames in advancing sequence without showing the hydraulic lines shown in FIG. 1.

FIG. 5 diagrammatically illustrates the advancing motions in three successive advancing cycles.

Referring now to FIG. 1, there is shown the advancing cylinders arranged at the front ends of the seam floor caps or beams associated with each of two frames A and each of two frames B in the position in which the frames B after completion of the advancing cycle during which the guide means of the mining equipment is advanced by the frames A assume the function of advancing the mining equipment. The hydraulic lines which are associated with the left-hand pair of frames A, B and which feed the props of the pair of frames are illustrated. The valves'associated with these hydraulic lines are shown in the positions to which they are switched for initiating the start of a new advancing cycle. Similar branch lines (not shown) and similar valves (not shown) are likewise connected to and used for the right-hand pair of frames A, B and for any and all other pairs of frames which may be used. All the branch lines and valves are fed by the main hydraulic lines 1, 2, 7, 8, 9 and 10 which are illustrated in the drawing, these main hydraulic lines are connected to the main control station and extend over the whole length of the mine working face.

In order to show the cooperation of the control elements with maximum clarity, the valves are not depicted on the frames but above the latter, and the props associated with the left-hand pair of frames are shown together with the branch lines which feed them, at the top of the Figure.

Referring to the drawings, the advancing cylinders associated with frames A and B and fixed for example to the caps or beams of the latter, are, like the advancing cylinders described in the prior referred to application, equipped with differential pistons. The only difference is that, in the case of the present form of construction, the smaller piston surface, i.e., the annular piston surface, is associated with the working-face-side chambers 327 and 327 of the advancing cylinders in the case of frames A and frames B, while the full piston surface is associated with the back-side chambers 326 and 326'. Also analogously with the prior referred to Application, the chamber with which the annular piston surface is associated is continuously fed with fluid pressure medium from the hydraulic line which passes through the longwall face. As this main hydraulic line now acts on the working-face-side chambers 327 and 327' of the advancing cylinders, it is no longer shown as main hydraulic line 3 but as main hydraulic line 10.

The main hydraulic line 10 is connected to each chamber 327 and 327' by an hydraulic branch line 10'. The back-side chambers 326 and 326' of each frame A, B are alternately acted on by the full hydraulic pressure of the system and released of the pressure through branch hydraulic lines 11 and 12 associated with this chamber. This either causes the piston associated with the advancing cylinder concerned to move forward, or outwardly of its cylinder, 01' causes this piston to be at its back side relieved of fluid pressure medium, with the result that the piston of the advancing cylinder concerned is retracted. The charging of the chambers 326 and 326' is affected by a step limiting assembly which is shown between the main lines 1, 2, 9, and 7, 8, 10. The rate at which the mining equipment is advanced at any given time can, therefore, be exactly determined by appropriately metering the fluid pressure medium charging the chambers 326 and 326' through the branch hydraulic lines 11 and 12. On the other hand, the chambers 327 and 327' are charged and the chambers 326 and 326' emptied without the interposition of metering devices so that the retracting of the piston, (i.e., the advancing of the cylinder and of the respective frame associated with the cylinder can take place appreciably more quickly.

The pistons of all the advancing cylinders are directly or indirectly connected to a guide means 201 of the mining equipment which extends through the entire length of the longwall face so that, when the pistons associated with the frames A or B which are set at any given time are moved outwardly of their cylinders, the guide means 201 is advanced. The guide means 20K carries with it, for a distance corresponding to a working stroke of the pistons or the piston rods respectfully, the frames B or A if they are in their released condition at this particular time. As the pistons associated with the advancing cylinders of the released frames B or A are retracted at the same time as theguide 201 is advanced, the forward movement of the released frame will also be accelerated correspondingly.

If a guide means 201 for mining equipment is provided both at the roof of the seam and at the floor of the seam, then an advancing cylinder has to be provided both for the seam roof cap of each frame A and B and also for the seam floor cap of the frame. Similarly, the number of branch hydraulic lines 10', 11 and 12 and the number of the valves which are connected in front of branch hydraulic lines 11 and 12 have to be doubled. I

The filling and emptying of the chambers 326 and 326 is controlled by applying full hydraulic pressure to the hydraulic lines 11 and 12 or by establishing communication between them and a discharge line 9 which runs for the length of the working face. The discharge line 9 simultaneously serves to reduce, by way of branch lines 9, excess pressure applied to the props. This discharge line 9 has already been per se disclosed in as yet unpublished German Patent application No. P 17 83 070.5 wherein valves 234 are shown to be controlled by the main hydraulic lines 7 and 8 and serve as step or pacelimiting assemblies. This publication also discloses four passage two-position valves 235 which are controlled by the main hydraulic lines 1i and 2. Naturally, the last-mentioned four passage two-position valves must be differently controlled in the present instance, so that the time intervals during which the frames A and B are set can mutually overlap.

As is the case of the prior referred to US. application, the present invention utilizes a main hydraulic line l which extends over the whole length of the working face and which supplies the props of the frames A, and also a main hydraulic line 2 which supplies the props of the frames B. In order to set the frames, these main hydraulic lines are fed with the full pressure of the hydraulic system, for example 240 atm., this pressure being applied to the props by way of branch hydraulic lines ll, 2'. Controllable check valves 22 are incorporated in these branch lines. According to the prior referred to US. application, the valves 22 connected before the props of frames A, B are opened when, and only when, a hydraulic line 1 or 2 is supplied with the full hydraulic pressure of the system. When the check valves are thus opened, the frames A, B can be relieved of pressure, the fluid pressure medium then discharges from the props into the main hydraulic lines 1 or 2 which are then only subject to a pressure of 20 atm. If the check valves were not opened in this manner, the frames which had just been set would also remain in their set condition, subject to the full pressure of the hydraulic system, if the main hydraulic line were to rupture.

In accordance with the present invention, the frames A, B are set and released subject to a similar method of control, but there is the sole difference that, instead of main hydraulic lines 4 and 5 being provided for closing and opening valves 22 and being suitably controlled from the main control station, branch hydraulic lines 4' and 5 are provided which, according to the switching control of the two-position four-passage valves 235 associated with each frame, are either supplied with the full pressure of the hydraulic system or are relieved of pressure. The pressure medium is fed by way of main hydraulic lines 7 and 8 which simultaneously control a metering device. Thus, the main hydraulic line 7 is supplied with the full system pressure when the main hydraulic line 8 is pressure-relieved and vice versa, these two oppositely-operating conditions following one another in alternating sequence. 0n the basis of the above-described example, such a change-over would occur each second.

The fluid pressure medium passes from the hydraulic line 7 to the metering cylinder 234 via the hydraulic line 7' which incorporates the check valve 107. The piston of the metering cylinder 234 is consequently moved to the left, with the result that the fluid pressure medium is forced from the left-hand chamber of the metering cylinder 234 into the hydraulic line 8 which conveys it to the four passage two-position. This is because the controlled check valve 118 is opened by the pressure effective in the branch hydraulic line 7".

As soon as this main hydraulic line 7 is relieved of pressure and the main hydraulic line 8 is supplied with the full pressure of the hydraulic system, the fluid pressure medium moves in the opposite direction into the metering chamber 234 via a hydraulic line 8 which incorporates a check valve 108 so that the piston of this metering cylinder 234 is shifted to the right. As a result, fluid pressure medium is thrust from out of the righthand chamber of the metering cylinder into the hydraulic line 7 which passes it to the four passage two-position 235. This is because the controlled check valve 117 is opened by the pressure effective in the branch hydraulic line 8".

If the main hydraulic lines 1 or 2 are now subject to the full pressure of the hydraulic system, the valve 235 is shifted towards the left by the pressure in the branch hydraulic line 1" (2") while, when the main hydraulic line 1(2) is relieved of pressure, the pressure of spring 235' causes the shifting of the valve to the right. The drawing shows the valve 235 associated with frame B in its left-hand position, as the main hydraulic line 2 is subject to full pressure. The valve 235, however, which is associated with frame A is shown in its right hand position as the main hydraulic line 1 is pressure-relieved. In the frame B which is set under the full hydraulic pressure of the system, the hydraulic line,

which arrives from the metering cylinder 234 and to which the full pressure of the hydraulic system is applied, is brought into communication with a branch hydraulic line 12; that is to say, the back-side chamber 326' of the advancing cylinder is placed under pressure and the piston of this advancing cylinder is thrust outwardly of the latter, while the hydraulic line 5' is brought into communication with the hydraulic line 209. The controlled check valves 22 at the props of frames B are therefore independent of the position of the valve which will be discussed below in a position which prevents, by a blocking action, the set props from being relieved of pressure. Thus, the frames B are set and the pistons of their advancing cylinders cause a metered forward movement of the mining equipment to take place.

On the other hand, the passage four 2-position valve 235 associated with the released frame A is, as shown in the drawing, shifted to the right under the pressure of the spring 235' which is greater than the pressure of 20 atm. effective in the branch hydraulic line 1". The hydraulic line which is connected to the metering cylinder 234 and which is subject to the full pressure of the hydraulic system therefore communicates with hydraulic line 4'. The controlled check valves at the props of frames A are thus opened, so that the frames continue to be subject to the reduced pressure of 20 atm. At the same time, the hydraulic line 11 is connected to a line 209, which causes the back-side chamber 326 of the advancing cylinder to be brought into contact with the hydraulic discharge line. The pressure applied by the hydraulic branch line 10' to the face side chamber of the advancing cylinder causes the piston of the advancing cylinder to be retracted into the latter. The frames A are thus brought into contact with the guide means 201 until their advancing cylinders abut this guide. This position of the frames is illustrated in FIG. 2, from which it will be seen that the frames B are still in their rearward position while the frames A are positioned further forward by a distance corresponding to one half step. The frames A are also now set, with the result that the guide 201 of the mining equipment moves away' both from the frames B which have been advancing it and also from the frames A. Both the main hydraulic line 1 and also the main hydraulic line 2 are fed with full pressure and all twoposition four-passage valves are shifted into their lefthand position.

If the step limiting assemblies which continuously execute reciprocating motions are disregarded, all the valves associated with the frames A will now be in the same position as the valves associated with frames B (see FIG. 1). Chambers 326 of the advancing cylinders thus start to be charged with fluid pressure medium at the same rate the fluid pressure medium is discharged from chambers 327.

At the end of the advancing cycle the position shown in FIG. 3 is arrived at. The pistons of the advancing cylinders fixed to frames B are in their fully extended positions. Guide 201 of the mining equipment is 1% steps in front of the frames B which are still set, and one half step in front of frames A which are already (newly) set. The pressure acting on the main hydraulic line 2 is now reduced from 240 atm. to 20 atm. The valves associated with the frames A now maintain their position so that the advancing motion of the guide means 201 proceeds without delay at the same rate. The valves associated with frames B, on the other hand, are now in the position which the valves associated with frames A had assumed in FIG. 1.

Thus FIG. la to 4 illustrate the pair of frames which acts on the same section of the guide of the mining equipment in subsequent phases: FIG. 1a shows it in the same position as FIG. 1; FIG. 2 shows it after conclusion of the first phase of the first advancing cycle; FIG. 3 shows it at the end of this advancing cycle; and FIG. 4 shows it after conclusion of the first phase of the next advancing cycle. In the next phase, that means at the end of the next advancing cycle, a position analogous to that illustrated by FIGS. 1 and 1a is attained, although both the frames A and also frames B and the guide of the mining equipment have been advanced by two steps or paces, if the distance moved forward by the mining equipment during each advancing cycle is designated as one step or pace. The two phases of each advancing cycle are of the same length in the embodiment illustrated and the excess length of the working stroke of the pistons of the advancing cylinders therefore amounts to half the length of a single step or pace.

In this way the position illustrated in FIG. 4 is arrived at. The guide 201 of the mining equipment is now 1% steps in front of frames A, which have maintained their positions illustrated in FIG. 2 and 3. The released frames B abut the guide 201, that is to say, they are forwardly positioned by a distance corresponding to two steps relative to their position in FIG. 3. They are now set, so that all the valves associated with frames B and frames A once again assume that position which the valves associated with frames B are shown as occupying in FIG. 1.

FIG. 5 illustrates the manner in which, during three successive advancing cycles, chambers 326' of frames B (upper row) and chambers 326 (lower row) are charged and discharged. Hatching formed of lines extending from lower right to upper left indicates that the chambers are being emptied, hatching whose lines extend from lower left to upper right indicates that the chambers are being filled subject to the action of the step limiting assembly, while cross-hatching indicates that the charging of the chamber is continuing and that the guide of the mining equipment, which is supported from the set frames, is being simultaneously moved forward. Seven vertical lines a to g show the start and end of the individual phases of the advancing cycle, each of which phases is started and ended by a changeover initiated at the main control station in the connections of the main hydraulic lines 1 and 2. The operation is therefore as follows:

a. First of all, the main hydraulic line 2 is switched to a pressure of 240 atm., and the main hydraulic line 1 is switched from a pressure of 240 atm. to 20 atm. The position illustrated in FIG. 1 is thus attained. The guide 201 of the mining equipment is advanced by the set frames B and draws the released frames with it; these frames A are simultaneously brought into a position in which they abut the guide 201 owing to the fact that the chambers 327 are charged from the main hydraulic line and to the fact that the chambers 326 are fully discharged. The position illustrated in FIG. 2 is thus arrived at.

b. The main hydraulic line 1 is switched from atm. to 240 atm. Guide 201 continues to be moved forward by frames B. At the same time, frames A are set and the chambers 326 of their associated advancing cylinders are filled with hydraulic pressure medium at the same rate as chambers 326, while chambers 327 and 327' are relieved by hydraulic pressure medium to a corresponding extent. Finally, frames A are reliably set and are now subject to the full pressure of the hydraulic system. The pistons of the advancing cylinders associated with frames B are in their fully extended position, so that the position illustrated in FIG. 3 has been reached.

c. The main hydraulic line 2 is switched over from 240 atm. to 20 atm. The guide 201 of the mining equipment is advanced by the set frames A and pulls the released frames B after it. These frames B are, at the same time, brought up so that they abut guide 201 owing to the fact that the chambers 327 are charged with hydraulic pressure medium from the main hydraulic line 10 and to the fact that the chambers 326' are completely emptied of fluid pressure medium. In this way the position illustrated in FIG. 4 is arrived at.

d. The main hydraulic line 2 is switched from pressure of 20 atm. to one of 240 atm. The guide 201 continues to be moved forward by the frames A. At the same time the frames B are set, and the chambers 326' of the advancing cylinders associated with them are filled with fluid pressure medium at the same rate as the chambers 326 of frames A. Finally, the frames B are reliably set subject to the full pressure of the hydraulic system, the pistons of the advancing cylinders associated with frames A being fully extended in these cylinders, and a position is once again attained such as corresponds to that shown in FIG. 1.

e. The main hydraulic line 1 is switched from 240 atm. to 20 atm. so that step (a) above is repeated.

f. The main hydraulic line is switched over from 20 atm. to 240 atm. so that step (b) is repeated.

g. The main hydraulic line is switched from 240 atm. to 20 atm. so that step (0 above is repeated.

According to a further modification of the invention, the above-described control system can be further complemented by a safety means which ensure that, should the main hydraulic lines 1 or 2 become defective, the whole working face will not collapse. As a consequence of the main hydraulic lines 1 or 2 being relieved of pressure, the corresponding two-position four-passage valve 235 comes into a switching position which causes the branch hydraulic lines 4', 5' respectively to be subject to the full pressure of the hydraulic system and consequently causes the controllable check valves 22 which are associated with the branch hydraulic lines 1' or 2 to be opened. It would be possible, if the main hydraulic lines 1 or 2 were to become defective or ruptured, for the frames A03) to be released at a point of time at which the frames B(A) are also released. In order to prevent this situation from arising in practice, valves 104 and 105 are arranged to cooperate with the hydraulic lines 4' and 5, respectively. More specifically, these valves 104 or 105 block any flow of hydraulic pressure medium in the direction of the controllable check valves 22 as long as the piston of the valve 104(105) is not shifted under the effect of the full setting pressure effective in the branch hydraulic lines 302, 301 of the other main hydraulic line 2, 1 into its terminal position in which it allows flowthrough of the fluid pressure medium. Thus, this means that the controllable check valves 22 associated with the frames A can only be opened when the props of the frames B are acted on by the full pressure of the hydraulic system, and vice versa. In order to ensure that the hydraulic lines 4' and 5' can also be relieved of pressure when the valves 104 or 105 block further infeed of the fluid pressure medium, it will be found convenient to arrange for a hydraulic line 109 to branch off, between the controllable check valves 22 and the valves 104 and 105 from the hydraulic lines 4' and 5 and to communicate with a hydraulic discharge line 9. This hydraulic line 109 also passes through the valve 104 or 105, although the piston of the valve allows the pressure medium to pass through hydraulic line 109 when this piston blocks flow of fluid pressure medium through hydraulic line 4 or 5', and vice versa. Thus, valves 104 and 105 automatically allow the fluid pressure medium to discharge when the valve performs a blocking action, to prevent the controllable check valves 22 from being acted on by the fluid pressure medium, and vice versa.

If each frame is provided with two advancing cylinders, one of these cylinders at the cap or beam of the seam roof and the other at the cap of the seam floor, then each of these frames will also be equipped with two hydraulic lines and l1, 12, with two of the four two-position four-passage valves 235 and with two step limiting assemblies. On the other hand, the hydraulic lines 4' or 5 and the valves 104 and 105 associated, respectively, with these hydraulic lines do not need to be duplicated. They must, however, each comprise an hydraulic connection to the controllable four two-position four-passage valves associated with the cap of the seam roof and with the cap of the seam floor, as well as an hydraulic connection to the controllable check valves 22 which cooperate with the individual props.

What is claimed is:

1. An improved self-advancing hydraulic mine roof support comprising at least two frames A and B all of which are operatively associated with a conveying or winning means and each of which is associated with a mine roof support; hydraulic fluid system pumping means; conduit means connecting said frames to said pumping means; valve means disposed in said conduit means; wherein said frames contain a cylinder having a back-side chamber and a face-side chamber and a hydraulically activated piston in said cylinder connected to said conveying or winning means by piston rods, step limiting assembly means adapted to equally reduce the feed of hydraulic fluid to said back side chambers and including means to sequentially;

a. feed high pressure hydraulic fluid into the faceside chamber of the cylinders of said frames A and into the back-side chamber of the cylinders of said frames B while maintaining said frames B immobilized between a mine floor and a mine roof whereby releasing a roof supporting position of and advancing said frames A to said conveying or winning means and additionally advancing said conveying or winning means, said frames A and said pistons and piston rods while maintaining said frames B stationary;

b. feed high pressure hydraulic fluid into the backside chamber of the cylinders of both of said frames A and frames B whereby to set frames A and to advance said conveying or winning means and said piston rods while maintaining all frames A stationary;

c. feed high pressure hydraulic fluid into the backside chamber of the cylinders of said frames A and into the face-side chamber of the cylinders of frames B while maintaining said frames A immobilized between said mine floor and said mine roof whereby releasing the roof supporting position of and advancing said frames B to said conveying or winning means and additionally advancing said conveying or winning means, frames B and the piston rods of both frames while maintaining said frames A stationary;

d. feed high pressure hydraulic fluid into the backside chambers of the cylinders of both of rames A and B whereby setting said frames B advancing said conveying or winning means and said piston rods while maintaining all of said frames stationae. and repeating step (a).

2. An improved mine roof support as claimed in claim 1 wherein said pistons are differential pistons, wherein the face-side chamber of the advancing cylinders thereof is associated with an annular surface of said piston, wherein said piston is continuously acted on through a main hydraulic line which extends along a working face by the full pressure of the hydraulic system, and wherein a full working face of the piston is associated with the back-side chamber of the advancing cylinders, which are associated with the frames A and B, serve to advance said conveying or winning means and also cause the frames B or A when released to overtake the frames A or B, respectively, and in which the full surface of the piston is acted on in frame A by a first hydraulic line and in the frame B by a second hydraulic line, each frame A and B having associated with it a valve arrangement controlled by branch lines of said main hydraulic lines, charging or relieving the props of said frames, respectively, whereby said valve arrangement acted on by an hydraulic line charging the props of the frames A(B) ensures that the line acting on the backside of the associated advancing cylinder communicates with a main hydraulic line supplying full pressure of the hydraulic system, and the valve arrangement acted on by an hydraulic line relieving the props of the frame B( A) ensures that the line acting on the back-side of the associated advancing cylinder conversely communicates with an hydraulic discharge line.

3. An improved mine roof support as claimed in claim 2, having a valve arrangement including at least one two-position four-passage valve for controlling a first hydraulic line and a third hydraulic line or a fourth hydraulic line and a second hydraulic line respectively.

4. An improved mine roof support as claimed in claim 3, including spring means associated with said two-position four-passage valve for for positioning such.

5. An improved mine roof support as claimed in claim 4 including means for blocking any flowthrough of the fluid pressure medium in the lines in the direction of the controllable check valve as long as the piston of a valve associated with these lines is free from the biasing force of said spring and under the effect of the full setting pressure effective in such lines into a terminal position wherein it allows the flowthrough of fluid pressure, the same valve, when its piston is in its other terminal position, being arranged to allow the direction. 

1. An improved self-advancing hydraulic mine roof support comprising at least two frames A and B all of which are operatively associated with a conveying or winning means and each of which is associated with a mine roof support; hydraulic fluid system pumping means; conduit means connecting said frames to said pumping means; valve means disposed in said conduit means; wherein said frames contain a cylinder having a back-side chamber and a face-side chamber and a hydraulically activated piston in said cylinder connected to said conveying or winning means by piston rods, step limiting assembly means adapted to equally reduce the feed of hydraulic fluid to said back side chambers and including means to sequentially; a. feed high pressure hydraulic fluid into the faceside chamber of the cylinders of said frames A and into the back-side chamber of the cylinders of said frames B while maintaining said frames B immobilized between a mine floor and a mine roof whereby releasing a roof supporting position of and advancing said frames A to said conveying or winning means and additionally advancing said conveying or winning means, said frames A and said pistons and piston rods while maintaining said frames B stationary; b. feed high pressure hydraulic fluid into the backside chamber of the cylinders of both of said frames A and frames B whereby to set frames A and to advance said conveying or winning means and said piston rods while maintaining all frames A stationary; c. feed high pressure hydraulic fluid into the back-side chamber of the cylinders of said frames A and into the face-side chamber of the cylinders of frames B while maintaining said frames A immobilized between said mine floor and said mine roof whereby releasing the roof supporting position of and advancing said frames B to said conveying or winning means and additionally advancing said conveying or winning means, frames B and the piston rods of both frames while maintaining said frames A stationary; d. feed high pressure hydraulic fluid into the back-side chambers of the cylinders of both of rames A and B whereby setting said frames B advancing said conveying or winning means and said piston rods while maintaining all of said frames stationary; e. and repeating step (a).
 2. An improved mine roof support as claimed in claim 1 wherein said pistons are differential pistons, wherein the face-side chamber of the advancing cylinders thereof is associated with an annular surface of said piston, wherein said piston is continuously acted on through a main hydraulic line which extends along a working face by the full pressure of the hydraulic system, and wherein a full working face of the piston is associated with the back-side chamber of the advancing cylinders, which are associated with the frames A and B, serve to advance said conveying or winning means and also cause the frames B or A when released to overtake the frames A or B, respectively, and in which the full surface of the piston is acted on in frame A by a first hydraulic line and in the frame B by a second hydraulic line, each frame A and B having associated with it a valve arrangement controlled by branch lines of said main hydraulic lines, charging or relieving the props of said frames, respectively, whereby said valve arrangement acted on by an hydraulic line charging the props of the frames A(B) ensures that the line acting on the back-side of the associated advancing cylinder communicates with a main hydraulic line supplying full pressure of the hydraulic system, and the valve arrangement acted on by an hydraulic line relieving the props of the frame B(A) ensures that the line acting on the back-side of the associated advancing cylinder conversely communicates with an hydraulic discharge line.
 3. An improved mine roof support as claimed in claim 2, having a valve arrangement including at least one two-position four-passage valve for controlling a first hydraulic line and a third hydraulic line or a fourth hydraulic line and a second hydraulic line respectively.
 4. An improved mine roof support as claimed in claim 3, including spring means associated with said two-position four-passage valve for for positioning such.
 5. An improved mine roof support as claimed in claim 4 including means for blocking any flowthrough of the fluid pressure medium in the lines in the direction of the controllable check valve as long as the piston of a valve associated with these lines is free from the biasing force of said spring and under the effect of the full setting pressure effective in such lines into a terminal position wherein it allows the flowthrough of fluid pressure, the same valve, when its piston is in its other terminal position, being arranged to allow the flowthrough of fluid pressure medium in the opposite direction. 